1. Field of the Invention
The present invention relates to an engine control system.
2. Description of Related Art
An ECU (an ECU arrangement) for controlling an engine is used to control multiple control target apparatuses relating to an engine control, and to control a part of functional units that are installed in a vehicle. The control target apparatuses include a fuel injection apparatus, a supercharger, an EGR apparatus, etc. The functional units include a safety device, an amenity-improvement device, etc.
The ECU controls each of the control target apparatuses according to an operational state of the engine and the like.
Recently, control of the control target apparatuses is liable to become more complex to achieve an advanced control.
Specifically, the fuel injection apparatus for a diesel engine is used as one of the control target apparatuses. Recent tightening of regulations for exhaust gases enhances the needs of pilot injections and multiple injections. A degree of accuracy of an injection quantity and an injection timing of each injection also needs to be improved. Thus, multiple correction processes and data for correction (e.g., a map) for each injection are needed. Therefore, an optimization process of each injection becomes complex. This results in an increase in a computation load of the ECU.
This is not limited to the fuel injection apparatus. The control programs for other apparatuses, such as for the supercharger and the exhaust gas recirculation (EGR) apparatus, are liable to become complex.
The first disadvantage will be described. There may be a case where one of the control target apparatuses, which are related to the engine control, is changed to a different-version control target apparatus. For example, the control target apparatus, which the ECU has controlled up to this time, is replaced with a newly developed control target apparatus or a control target apparatus of other company. Specifically, there may be an assumed case where the fuel injection apparatus, which is one of the control target apparatuses, is replaced with a newly developed advanced apparatus to improve an engine performance (e.g., exhaust emission control performance).
Even in the case where only one control target apparatus is replaced like wise, the whole ECU needs to be replaced, because a conventional ECU is constituted as a single unit.
The ECU as the single unit means that a control unit includes a single computer.
As described above, the ECU controls the multiple control target apparatuses for the engine control and a part of the functional units, which are installed in the vehicle. Thus, the ECU needs an enormous amount of control programs.
Therefore, when only one control target apparatus needs to be replaced, the whole ECU, which needs the enormous amount of control programs, needs to be replaced. Thus, this necessitates enormous manpower for development, and this results in an enormous cost. This makes it difficult to improve the engine function through replacement of one control target apparatus with other control target apparatus.
The second disadvantage will be described. As a countermeasure for the above-described inconvenience, the ECU may be divided into a main ECU and sub-ECUs. The main ECU performs a basic computation. Each sub-ECU controls a corresponding control target apparatus based on an operational command value, which is calculated by the main ECU.
However, the following disadvantages are caused, when the sub-ECU specifically controls a specific control target apparatus based on the operational command value of the main ECU.
For example, when a learning operation of the control target apparatus, which the sub-ECU controls, is performed, the control target apparatus needs to be operated at a special operational state, which is suitable for the learning operation.
Specifically, when the learning operation is performed for the fuel injection apparatus, a special engine operational state, which is suitable for the learning operation, may need to be set. The special engine operational states include, for example, a special idling and a check operation with a check command.
In this case, the main ECU needs to calculate the operational command value, which sets up the special engine operation. In order to achieve this, the main ECU more closely relates with the fuel injection apparatus. This may eliminate an advantage of installing the divided sub-ECU, or the sub-ECU that directly controls the control target apparatus.
The third disadvantage will be described. When the learning operation is performed, the main ECU sets up the special engine operational state, which is suitable for the learning operation. Thus, an operation of the control target apparatus during an “interval between a start and an end of the learning operation” depends on the main ECU.
An opportunity to perform the learning operation while driving the vehicle is usually not often and also limited to a short time. Thus, the learning operation is often not finished.
Therefore, when the operational state becomes suitable for the learning operation, the learning operation needs to be performed as soon as possible.
However, in a case where the main ECU performs the learning operation, a possibility of finishing the learning operation becomes lower, because a control logic interrupt latency at the main ECU occurs.
As described in the above learning operation, the sub-ECU depends on a control command of the main ECU, even when the ECU is divided into the main ECU and the sub-ECU. This results that the two ECUs control the control target apparatus. Therefore, the sub-ECU cannot freely control the control target apparatus.
In other words, a control range for the sub-ECU to control the control target apparatus is always limited by an operation of the main ECU. Therefore, the advantage, which is caused by dividing the ECU into the main ECU and the sub-ECUs, is not substantially maximized.